1. Field of the Invention
Embodiments of the disclosure relate to a display device, and more particularly, to a display device, which can change a frame frequency based on the properties of a display image.
2. Discussion of the Related Art
Known display devices for image display include a cathode ray tube, a liquid crystal display LCD, an organic light emitting diode OLED, a plasma display panel (PDP), and an electrophoretic display (EPD).
The display devices include a display panel on which pixels and signal lines are formed, a driving circuit unit for driving the signal lines of the display panel, and a power voltage generating circuit for generating a power voltage required to drive the driving circuit unit.
The signal lines comprise data lines supplied with data voltages and gate lines supplied with gate pulses for selecting pixels supplied with data voltages. The driving circuit unit comprises a data driving circuit for driving the data lines and a gate driving circuit for driving the gate lines. The power voltage generating circuit supplies a data power voltage to the data driving circuit, and supplies a gate high voltage and a gate low voltage (a gate power voltage) to the gate driving circuit. The data power voltage is fixed, and the gate power is fixed.
For such a display device, the technology for changing the frame frequency according to the properties of a display image is known. In this technology, the frame frequency of a dynamic image showing a relatively large change in the image between adjacent frames is controlled to be a first value (e.g., 60 Hz), and the frame frequency of a static image showing a relatively small change in the image between the adjacent frames is controlled to be a second value (e.g., 40 Hz). The displaying of an image at a frame frequency of 40 Hz has the advantage of lower power consumption compared to the displaying of an image at a frame frequency of 60 Hz.
As shown in FIG. 1, when the frame frequency is changed, 1 horizontal period (1H), i.e., charging time, for charging a data voltage in the pixels is varied. The charging time at the frame frequency of 40 Hz is longer than the charging time at the frame frequency of 60 Hz. As a result, the charging amount CA2 at the frame frequency of 40 Hz is more than the charging amount CA1 at the frame frequency of 60 Hz. In realizing the same gray level, a charging amount difference depending on frame frequency causes a change in the luminance of the display image, thereby degrading the display quality. In FIG. 1, ‘GP’ represents a gate pulse, and ‘CP’ represents a data voltage charging pulse.
The reason why the charging amount varies depending on frame frequency is because the power voltage required for driving the driving circuit unit is generated at a fixed level. Particularly, if the frame frequency is decreased from 60 Hz to 40 Hz when the power voltage is fixed, the effect of power consumption reduction is not high.